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Water management

Is your water working hard enough for you?

As all growers know, making the most of this valuable and limited resource is critical. This water management advice from CottonInfo is designed to help you make the most of your water: achieving maximum production from available water resources in any given season.

What do you need to know?

Water use efficiency:

Water Use Efficiency (WUE) is a term that is commonly used to describe the relationship between production (eg. bales of cotton) and the water input in megalitres used to grow the crop. WUE is also used to describe the efficiency of water delivery, application and use. Reducing water losses while maximising crop yields will increase WUE, improving total farm profitability. Creating a whole farm water management plan and implementing a water budget are integral to optimising WUE.

Water budgeting:

A water budget is used to determine how best to use the available water resource, where the availability of the resource may vary significantly during the season due to rainfall. The water budget determines the area of crop to be planted given the water resources available at the beginning of the season. The budget also calculates how to use crop inputs during the season as water availability changes (including determining when to plough out crops due to insufficient water availability).

Irrigation system design:

The design layout of fields, storages and channels are a significant influence on farm WUE. There are four irrigation system designs, with furrow irrigation being the main one use in cotton. Alternative systems can reduce labour costs and allow for more precise water application, however systems must be designed, installed and managed correctly to maximise WUE.

Furrow irrigation: Over the bank siphon/furrow irrigation is well suited to cracking clay cotton soils, with fully optimised siphon systems achieving performance levels similar to overhead systems. Small changes in management may increase WUE significantly: irrigation flow rates and cut off times should be managed to maximise application efficiency and distribution uniformity, which will reduce runoff, deep drainage and loss of nutrients. For more, read the CottonInfo furrow irrigation fact sheet, found under Publications below.

Centre Pivot Lateral Move (CPLM): CPLM systems can apply small amounts of water at each application, allowing for more frequent irrigations to meet crop water demand. These systems can reduce labour requirements, but on-going energy costs will be higher than surface systems and should be carefully considered in any investment decision. For more, read the Centre Pivot Lateral Move report, found under Publications below.

Subsurface Drip (SSD) irrigation: SSD irrigation systems require a significant capital investment making reliable of water supply an important consideration. SSD systems usually operate at lower pressure than other irrigation systems, reducing energy costs. SSD systems achieve very high WUE when operated correctly. For more, read the drip irrigation case study, found under Publications below.

Bankless channels: Bankless irrigation systems remove the need for siphons, significantly reducing labour requirements. Bankless systems also result in better machine efficiency. Structural design varies, but generally involves high flow rates with all furrows in each bay irrigated at once. However, there is no evidence that WUE is improved. For more, read the CottonInfo bankless channels fact sheet, found under Publications below.

The four types of irrigation system designs have been compared in a trial at ‘Keytah,’ Moree, conducted by the Gwydir Valley Irrigator’s Association (GVIA) (with support from CRDC, the National Water Commission and Sundown Pastoral Company). This is the only trial of its kind in Australia. You can read the findings in the Spring 2014 edition of the CRDC publication Spotlight.

Irrigation scheduling:

Irrigation scheduling refers to the timing and volume of water application to a crop. Good scheduling should meet the plants' water demand and should prevent over or under irrigation so that balanced growth is achieved.

Storage design & maintenance:

Effective storage design, management and location within an irrigation operation can minimise evaporation and seepage losses. Storages and channels require regular maintenance to ensure efficient operation, including visual inspection for leaks and seepage. Losses from storages should be measured and monitored to ensure early identification of problems that may require amelioration.

So, what should you do on your farm?

Keep records (volumes of water supplied to the farm, volumes of water harvested, rainfall, storage volumes and soil moisture) to examine current irrigation performance, improve farm water management and for water budgeting.

Monitor the weather conditions and forecasts, the plant and the soil to help schedule irrigations to meet crop water requirements and avoid plant stress.

Regularly maintain storages and channels to ensure efficient operation, including visual inspection for leaks and seepage

Storages should be surveyed to check capacity against original design and an accurate depth-volume calibration curve produced so that storage volumes can be accurately measured.

Reduce deep drainage and associated salinity and rising groundwater risk in early season irrigations by minimising the time available for infiltration – get water on and off quickly.

WaterTrack Rapid: provides a rapid and simple summary of water use performance over a season and total losses.

WaterTrack Divider: provides a summary of seasonal water use performance but divides total losses into storage, channel, drain, operational and in-field losses.

WaterTrack Optimiser: provides a comprehensive daily whole farm or whole system water balance, including a full break down of water use and losses for each element, plus the ability to predict water use and losses in a planted area.

HowWet: Windows based program which uses farm rainfall records to estimate how much plant water has been stored in the soil, and the amount of organic nitrogen converted to an available form during a fallow.

CropWaterUse: tool to aid in the development of a water budget, assists in determining how much water different crops require and recommended irrigation scheduling based on weather conditions.

Watersched 2: web based real-time tool developed to provide guide scheduling decisions by modelling root zone water depletion, based on real-time weather data from SILO and approved weather station networks.